Field of the Invention
The present invention relates to an illumination optical system, and to a spectrophotometric apparatus and an image forming apparatus including the same.
Description of the Related Art
In recent years, there has been developed an illumination optical system utilizing an ellipsoidal reflection surface that is effective for development of illumination efficiency.
In Japanese Patent Application Laid-Open No. 2014-94122, there is disclosed an apparatus configured to collect illumination light emitted from an optical fiber onto a sample with use of an ellipsoidal reflection surface.
In Japanese Patent Application Laid-Open No. 2014-17052, there is disclosed an apparatus configured to collect illumination light emitted from an LED with use of a hollow ellipsoidal reflection surface.
However, in the apparatus disclosed in Japanese Patent Application Laid-Open Nos. 2014-94122 and 2014-17052, the light source is arranged on a focal point of the ellipsoidal reflection surface. Therefore, when the light source is not arranged at a nominal dimension due to an arrangement error, the amount of light collected to an object is sharply decreased. That is, there is a problem in that the illumination efficiency is sensitive to the arrangement error of the light source. In the following, for the sake of easy description, arrangement at the nominal dimension is referred to as “nominal arrangement”, and arrangement not at the nominal dimension is referred to as “non-nominal arrangement”.
In particular, when the LED is used as the light source as in Japanese Patent Application Laid-Open No. 2014-17052, it is difficult to control the tolerance in positional variation of a light emitting portion inside the LED light source. Therefore, the variation in illumination efficiency due to the tolerance tends to be a problem.